1. Field of the Invention
The invention relates to a pixel unit, and more particularly to a pixel unit that does not be affected when an operation voltage is shifted.
2. Description of the Related Art
Because cathode ray tubes (CRTs) are inexpensive and provide high definition, they are utilized extensively in televisions and computers. With technological development, new flat-panel displays are continually being developed. When a larger display panel is required, the weight of the flat-panel display does not substantially change when compared to CRT displays. Generally, flat-panel displays comprises liquid crystal displays (LCD), plasma display panels (PDP), field emission displays (FED), and electroluminescent (EL) displays.
FIG. 1 is a schematic diagram of a conventional pixel unit. The pixel unit 100 comprises transistors 110 and 130, a capacitor 120, and a luminiferous device 140. When the transistor 110 is turned on by a scan signal SCAN, the capacitor 120 stores charge according to a data signal DATA. The transistor 130 provides a driving current to the luminiferous device 140 according to the stored charge. The intensity of the light, which emitted by the luminiferous device 140, relates to the amount of the driving current.
Generally, a power line is utilized such that pixel units receive an operation voltage PVDD. When the size of a display panel is increased, the length of the power line is also increased. Thus, the parasitical resistor of the power line is increased such that a voltage difference between two terminals of the power line is increased. For example, the voltage in one terminal of the power line maybe 5V and the voltage in another terminal of the power line maybe 4.5V due to the parasitical resistor of the power line. Since the driving current provided by the transistor 130 relates to the operation voltage PVDD, when the operation voltage PVDD is shifted, the driving current is affected. Thus, the intensity of the light, which emitted by the luminiferous device 140, is inaccurate.